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A research group in Germany has successfully inserted genetic material into the chloroplasts of a tomato plant, increasing the potential for edible medicines and reducing the risk of cross-pollination.

Chloroplasts are plastids - packages outside the cell nucleus that contain pigments, in this case the green pigment chlorophyll. It is the first time that foreign genes have been introduced into the plastids of a fertile food crop and transferred to the next generation.

Professor Ralph Bock and his team, based at the Institute for Plant Biochemistry and Biotechnology at the University of Münster, report their results in the current issue of Nature Biotechnology.

Plants have DNA in three places in their cells: most is concentrated in the nucleus, with a smaller amount in mitochondria and chloroplasts. Traditionally, geneticists place genes into nuclear DNA, but the DNA in chloroplasts, unlike nuclear DNA, is not transmitted in pollen.

This could alleviate a major concern about genetically modified crops - the risk of cross-pollination of neighbouring plants.

The German team used a marker gene to show the technique works. But if the method proves viable in production, another benefit could be the potential for 'medicinally enhanced' foods - containing vaccines, antibodies, and pharmaceuticals.

"What is important about the German research is the chloroplast method has a high level of protein production," said Professor James Dale, head of the Biotechnology Group at the Queensland University of Technology.

There is only one nucleus in a cell, but many chloroplasts, so transgenes that are inserted into chloroplasts exist at much higher levels. If the transgenes are a vaccine, for example, this increases the chances of producing a sufficient volume of antigen to be effective.

To date, however, researchers have had difficulty achieving high levels of chloroplast gene expression in the edible parts of the plant.

Australian researchers have been working on edible vaccines for some time. Professor Dale heads a research team working on vaccines in bananas, using standard nuclear DNA transformation.

"Essentially we insert the gene for a particular vaccine protein into a plant genome," he said.

Bananas are a good choice for edible vaccine research, explained Professor Dale, because they are sterile so genes do not pass from banana to banana. They are eaten raw, so vaccine proteins will not be degraded during cooking, and in addition, they have a relatively long shelf life and are widely grown and eaten in tropical and subtropical regions.

"In undeveloped countries where the health budget may be one dollar per person per year, this poses a great advantage to people who do not have access to good health care," Professor Dale said.